This invention generally relates to recyclable and repulpable coated paper stocks and related methods of making the same useful as packages, containers or labels having water resistance, grease resistance and moisture vapor barrier characteristics. More particularly, it concerns coated paper stocks, preferably for use as ream wrap, comprised of a substrate coated on at least one surface with a base coat and at least one additional coat over said base coat both of which are applied as wax free water based polymeric dispersions. The water based dispersion coatings are repulped and recycled more readily than conventional polyethylene or wax coatings.
Polyethylene films and wax coatings, which are generally laminated or coated to paper, are widely used in packaging applications to protect products from moisture and provide water or grease resistance. However, recycling of packaging containing polyethylene films and wax coatings are limited and costly since special equipment is necessary for repulping and various process steps are required prior to reintroducing such a slurry into a recycling stream along with office waste paper. In addition, polyethylene films and some wax coatings will not degrade if the package is composted. These problems are encountered in specific packaging application areas, for example, where such coatings are used in the production of ream wrap.
Conventional ream wraps are typically a multi-ply product having a center ply of polyethylene in between two ply""s of paper. Polyethylene is used in ream wraps to provide an effective barrier to water vapor (humidity) which can cause the wrapped paper to curl resulting in misfeeds and jams in copy machines or printing presses. These multilayered plastic film ream wraps cannot easily be recycled. Landfills and incineration are the common ways to dispose of polyethylene packaging materials. Alternatively, other coatings and coating systems are known which do not contain polyethylene but provide the level of moisture resistance necessary for ream wrap. For example, U.S. Pat. No. 4,117,199 to Gotoh et al. discloses a repulpable coated paper containing a synthetic rubber latex and a wax emulsion. Coatings such as Vapo-Stop, manufactured by Cham-Tenero Paper Mills, Inc., Cham, Switzerland, include a styrene-butadiene polymer, wax and acrylic polymer components which provide moisture resistance to coated substrates. These systems however contain a high loading of wax which make the formulation unacceptable for recycling as office waste and repulping for white paper production.
Thus it would be desirable to find an alternative for conventional polyethylene films and coatings containing wax that has comparable moisture barrier properties but also has the added benefit of repulpability and recyclablity.
U.S. Pat. No. 2,392,972 to Cheyney discloses surfacing of paper with a coating of vinylidene chloride-vinyl chloride copolymers to produce a coated paper which is resistant to the transmission of water vapor. Other representative patents which describe use of polyvinylidene chloride as a means for imparting water vapor resistance to paper include U.S. Pat. Nos. 3,476,587 to Demol et al. which discloses compositions comprising two vinylidene chloride copolymers, one hard and the other supple, to waterproof a substrate and U.S. Pat. No. 3,423,232 to Reinhard et al. which discloses coating flat substrates with aqueous dispersions including 80-98% vinylidene chloride polymers as a subcoating and top coating.
U.S. Pat. No. 3,306,766 to Hathaway et al. discloses a resin coated packaging product, preferably a paper based sheet, having the exposed surface thereof coated with a haloethylene polymer resin, such as saran, and an intermediate flexible foundation coating of extruded ethylene-lower alkyl acrylate copolymer resin. The haloethylene polymer resins, e.g. saran, are resistant to the passage of water vapor and include at least 60% by weight of polyvinylidene chloride resins.
From the prior art mentioned it is seen that coatings which include vinylidene chloride copolymers to provide a moisture barrier are known, however, the prior art does not provide a method for directly applying these coatings to a porous substrate. It would be appreciated that advantage over known applications would be obtained by providing wax free aqueous coatings directly applied to a substrate surface to impart water and water vapor resistance properties comparable to conventional polyethylene or wax coatings but are repulped and recycled more readily. The present invention is directed to the provision of such recyclable and repulpable coatings to produce a coated paper product for use as ream wrap. The water-based coatings of the invention provide an alternative to conventional polyethylene coatings and wax coatings and an advantage over the prior art since the coated paper can easily be repulped without special flotation equipment, which is needed when repulping polyethylene film. The water-based coatings disperse in water, allowing the paper fibers to be easily reclaimed for reuse. The invention coatings, unlike wax-coatings, are repulped and recycled along with office wastepaper to produce a high grade white paper.
Accordingly, it is a broad object of the invention to provide a recyclable and repulpable coated paper stock comprised of a substrate coated with a base coat and at least one additional coat over the base coat, both of which are wax free water-based polymeric dispersions.
An object of the invention is to provide a recyclable and repulpable coated paper stock which is formed into a package, container or label.
A more specific object of the invention is to provide a recyclable and repulpable coated paper stock, for use as ream wrap, having water resistance, grease resistance and moisture vapor barrier characteristics.
A specific object of the invention is to provide a coated paper stock that is readily recycled without dependence on special equipment for repulping.
A more specific object of the invention is to provide a coated paper stock that is readily repulped and recycled along with office waste paper to produce a high grade white paper.
In the present invention, these purposes, as well as others which will be apparent, are achieved generally by coating at least one surface of a substrate with a base coat and at least one additional coat over the base coat both of which are applied as water-based polymeric dispersions. Alternate embodiments include applying at least one further additional coat.
The base coat and additional coat or coats are free of any wax component and comprise a water-based dispersion of a polymer selected from the group comprising acrylic polymers, acrylic copolymers, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl acetate, polyvinyl chloride, styrene-butadiene copolymers, polyvinylidene chloride and its copolymers, or starch. Typically, the coatings comprise dispersions having a solids content greater than 20% and a viscosity in the range of 20 to 1000 cps.
In a preferred embodiment, the base coat comprises an acrylic modified poly(ethylacrylate) latex and the additional coat comprises polyvinylidene chloride or copolymers thereof. In another preferred embodiment the base coat and additional coat comprise polyvinylidene chloride or copolymers thereof. Additionally, in either embodiment at least one further additional coat of the same materials may be applied. The invention however is not limited to these embodiments, which are meant to be illustrative, but also include numerous variations thereof.
The base coat may additionally include pigments or mineral fillers, such as, but not limited to, aqueous dispersions of clay, calcium carbonate or mica. Other additional components of the coatings may include thickening agents, defoaming or antifoaming agents, pigments, crosslinking agents, slip additives, release agents and antiblocking agents.
Substrates employed in the invention are cellulose-based materials and include a variety of coated and uncoated paper and paperboard, including bleached or unbleached, hardwood or softwood, virgin or recycled, and clay coated or uncoated forms of paper or paperboard. The basis weight of the substrates are in the range of 20 to 150 lbs per 3,000 sq. ft. and the thicknesses range from 0.004 to 0.025 inches. A preferred substrate is paper and is selected from the group comprising bleached paper, clay-coated bleached paper, unbleached paper or recycled paper.
The coatings are applied to the substrate surface as aqueous dispersions. The coatings are dried on the substrate surface to form a pin-hole free continuous film on the substrate which is resistant to water and water vapor. Water vapor transmission rates of the coated stocks are typically in the range of 0.8 to 7 g/100 sq.in./24 hr, and preferably between 1 to 3 g/100 sq.in./24 hr. Depending on the composition of the base coat, the base coat is either partially dried or totally dried prior to the application of the additional coat.
The individual coating layers each have dry coating weights in the range of 1 to 8 lbs. per 3,000 sq. ft. The total dry coating weights on the substrate are in the range of 1 to 16 lbs. per 3,000 sq. ft.
The recyclable and repulpable coated paper stock of the invention is formed into a package, preferably ream wrap, having water resistance, moisture vapor barrier characteristics and grease resistance. In preferred applications the water-based coating corresponds to a moisture vapor barrier located in the internal structure of the package which prevents enclosed materials, such as copy paper, from warping or curling.
In other applications, the coating may be applied to the opposite side of a clay coated substrate and used as a label, where the clay coated side provides a printable surface and the invention coating provides barrier characteristics to the resulting container.
The wax free coatings of the invention are repulped and recycled more readily than conventional polyethylene or wax coatings. Advantageously, the coated paper stock can be added directly to an office waste paper recycling stream, without dependence on special equipment, to produce a high grade white paper.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description of the best mode of practicing the invention when considered with reference to the drawings, as follows: